Wednesday, March 3, 2010

Ecologists had been puzzling over the desert rhubarb for years: Instead of the tiny, spiky leaves found on most desert plants, this rare rhubarb boasts lush green leaves up to a meter wide.

Now scientists from the University of Haifa-Oranim in Israel have discovered that ridges in the plant’s giant leaves actually collect water and channel it down to the plant’s root system, harvesting up to 16 times more water than any other plant in the region.

“It is the first example of a self-irrigating plant,” said plant biologist Gidi Ne’eman, a co-author on the paper published in March in Naturwissenschaften, a German journal of ecology. “This is the only case we know, but in other places in the world there might be additional plants that use the same adaptions.”

The desert rhubarb grows in the mountainous deserts of Israel and Jordan, where there’s only about 75mm of rainfall each year. Even during the rainy season, the region’s light rainfalls often don’t penetrate the rocky soil of the desert. Plants with large leaves and a deep root system, like the desert rhubarb, typically can’t survive in such an arid climate.

But when the researchers measured the plant’s water absorption during a light rain, they discovered that water infiltrated the soil 10 times deeper around the desert rhubarb than in surrounding areas. Upon closer examination, scientists discovered deep grooves around the plant’s veins, which are coated in a waxy cuticle that helps channel water down to the root.

“Even in the slightest rains,” the researchers wrote, “the typical plant harvests more than 4,300 cubic centimeters of water per year and enjoys a water regime of about 427 millimeters per year, equivalent to the water supply in a Mediterranean climate.”

Some scientists say the desert rhubarb isn’t all that, however. “Many plants channel water to their base to be absorbed by the root,” Lindy Brigham, a plant ecologist from the University of Arizona, wrote in an email. “Just look at the way plant leaves are shaped and how they branch from the base in many cases.” The architecture of the desert rhubarb’s leaves is unusual, she said, but not necessarily the only example of this adaptation.